Its not true.
H1 is DUAL INTENT (to legally live and to legally work in US) visa
Where as H4 is SINGLE INTENT(to legally live as a dependent on another legal non-immigrant (in your case H1) visa holder) Visa.
While H1 is being owned by your employer(NOT YOU), H4 is being owned by you(the Applicant/beneficiary), Applying H4 doesnt diminish the H1 visa approval.
But while you apply for both in parallel, the later would conceal the former (in other words, if you apply for H4 now and got approved but later your pending H1 approved, you will be in H1 status. The same happens the other ways if H1 approved now, but H4 approved later, you will become H4(but you can withdraw H4 immediately if H1 approved before). But in any way, you will be eligible to travel to US as both visas had your SINGLE intent to legally live in US.